Laser Pulse Phenomena and Applications Part 14 potx

Hot Chemistry with Cold Molecules 381 second harmonic of Nd:YAG laser operating at a repetition rate of 1 kHz (Corona, Coherent Inc.). The chirped ultrafast laser pulses can be easily produced from our suitably modified compressor setup for the amplified laser system. As we increase the spacing between the compressor gratings relative to the optimum position for minimum pulse duration of 50 fs, we generate a negatively chirped pulse. Conversely, we obtain the positively chirped pulse by decreasing the inter-grating distance. Pulse durations were measured using a home- made intensity auto-correlation for the transform-limited pulse, as well as for the various negatively chirped and positively chirped pulses (Fig. 12). The pulses were further characterized by second harmonic frequency resolved optical gating (SHG-FROG) technique. Fig. 13a shows a typical SHG-FROG trace of our near transform-limited pulse that was collected using GRENOUILLE (Swamp Optics Inc.). In Fig. 13b retrieved spectra and phase of the transform limited pulse is shown. From this Fig. 13b is found that phase of the laser pulse is constant within the bandwidth of the laser pulse and hence it is made sure that at optimal grating distances we get the shorter pulse which is transform limited. In Fig. 14a, we show the SHG spectrum of the of the transform limited pulses after frequency doubling with 50 μm type-1 BBO crystals as well as the spectrum of the transform-limited pulse collected with a HR-2000 spectrometer (Ocean Optics Inc.). From the Fig. 14b, FWHM of the near transform limited pulse is found to be ~18 nm. The minimum time duration of a transform limited pulse giving a spectrum with ∆λ (18 nm) at FWHM, central wavelength (800 nm) and the speed of light (m/s) c: 2 0 tK c λ λ Δ= Δ⋅ where K is the time-bandwidth product ( K=0.441 for Gaussian pulse), ∆t is found to be 50 fs for 18 nm bandwidth pulse which is our transform limited pulse. The laser pulses are then focused with a lens (focal length = 50 cm) on a supersonically expanded molecular beam of n-propyl benzene at the centre of a time of flight chamber. The polarization of the laser was horizontal as it enters the mass spectrometer and is perpendicular to ion collection optics. The Mass spectra from our particular beam chamber constructed with dry-scroll pumps and turbo-molecular pump as described above has the advantage that it does not contain any extraneous water and hydrocarbon peaks and thus has better sensitivity for organic samples as reported here. -600 -400 -200 0 200 400 600 0.0 0.5 1.0 1.5 2.0 intensity (a. u.) delay (fs) 50 fs 150 fs 250 fs 350 fs 450 fs 550 fs Fig. 12. The various autocorrelation traces of the pulse for different chirps. Laser Pulse Phenomena and Applications 382 0 100 150 20050-150 -100 -50-200 370 380 390 400 410 420 430 Delay (fs) Wavelength (nm) 700 720 740 760 780 800 820 840 860 880 900 200 400 600 800 1000 spectrum of 800 nm phase wavelength (nm) Intensity (a. u.) 0.0000 0.0002 0.0004 0.0006 0.0008 0.0010 phase (a) (b) Fig. 13. (a) SHG-FROG trace of our near transform limited 50 fs pulse, (b) retrived spectra and phase of the transform limited pulse. 380 400 420 440 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Intensity (a. u.) wavelength (nm) 700 720 740 760 780 800 820 840 860 880 900 200 400 600 800 1000 intensity (a. u.) wave length (λ) Fig. 14. (a) SHG Spectrum of transform limited pulse, (b) spectrum of the transform limited pulse. Generation of Femtosecond chirped pulses: Femtosecond chirped pulse can be easily generated by the compressor setup. This pulse increases its frequency linearly in time (from red to blue). In analogy to bird sound this pulse is called a “chirped” pulse. Our compressor setup (Fig. 15) consists of a pair of grating and a high reflective mirror. Our compressor gratings have 600 grooves/mm (Newport), and have throughput efficiency of 60%. One of the gratings is placed on a translation stage. By changing the distances between the two gratings and carefully aligning the optical paths at some optimal position a shorter near transform limited 50 fs laser pulse is generated. The transform limited condition is confirmed by characterizing the laser pulses at transform limited condition by measuring the SHG-Frog and autocorrelation trace. As we increase the spacing between the two gratings relative to the optimum position we can generate negatively chirped pulse. Conversely if we decrease the inter-grating distance we can generate positively chirped pulse. Hot Chemistry with Cold Molecules 383 An incident laser pulse of spectrum E 0 (ω) will be shaped by the compressor setup and spectrum of the output will be E 0 (ω)e iφω . For a light pulse which is centered around ω 0 having a reasonably small bandwidth, the total phase can be expanded around ω 0 to second order in ω: 00 2 2 00 0 2 11 1! 2! () ( ) ( ) ( ) ωω ωω ϕϕ ω ω ϕω ϕω ω ω ω ω == ∂∂ ∂ ∂ ≈+ −+ − Here, the second order term is responsible for group velocity dispersion. In fact, 0 2 2 ω ω ϕ ω β = ∂ ∂ = is linear chirp coefficient (chirp parameter in the frequency domain) introduced by the compressor and is defined as second derivative of the spectral phase at the center frequency. The linear chirp coefficient (β) can be calculated using the equation: 2 22 0 0 4ln2 β τ ττ ⎡ ⎤ =+ ⎢ ⎥ ⎣ ⎦ where τ is the pulse duration of the chirped laser pulse and τ 0 is the chirp-free pulse duration of the transform limited pulse in FWHM. Pulse durations were measured by intensity autocorrelation technique. The experimental error in the chirp value calculated from the equation mentioned above is about ±9%. I O Fig. 15. Compressor setup, GR1, GR2- Garting, HR-high reflective mirror. 3. Results and discussions Our TOF design provides high resolution when it is used in conjunction with our skimmed supersonic molecular beam chamber. Fig. 16 shows the time of flight mass peak of n-propyl beanzene cation. This was taken using femtosecond laser photo-ionization at 800 nm. The resolution is defined as R = t/(2∆t), where t is the total flight time of the ion packet and ∆t is the FWHM of the peak. In the case n-propyl benzene cation resolution R is found to be around 1113. (Fig. 16) With careful adjustment of the voltages of the time of flight power supply and nozzle to skimmer distance to prevent turbulence on the skimmer, we have HR GR1 GR2 Laser Pulse Phenomena and Applications 384 observed ion packet widths of ~10 ns. Resolution R = t/2∆t = 22.1995/(2×0.0097) = 1113, our mass spectra can resolve the adjacent mass peaks in the range of m/z from 0 to 1113 amu. 22.05 22.10 22.15 22.20 22.25 22.30 22.35 22.40 22.45 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 ion intensity time (microsecond) Fig. 16. Ion peak of n-propyl benzene cation It has been known that the fragmentation processes in polyatomic molecules induced by an intense ultrafast laser field can sometimes exhibit sensitive dependence on the instantaneous phase characteristics of the laser field (Itakura et al., 2003; Pestrik et al., 1998; Mathur & Rajgara, 2003; Lozovoy et al., 2008, Goswami et al., 2009). Depending on the change in sign the chirped laser pulses, fragmentation could be either enhanced or suppressed. Controlling the outcome of such laser induced molecular fragmentation with chirped femtosecond laser pulses has brought forth a number of experimental and theoretical effects in the recent years. However, efforts are continuing for a specific fragment channel enhancement, which is difficult since it also is a function of the molecular system under study. Here we report the observation of a coherently enhanced fragmentation pathway of n-propyl benzene, which seems to have such specific fragmentation channel available. We found that for n-propyl benzene, the relative yield of C 3 H 3 + is extremely sensitive to the phase of the laser pulse as compared to any of the other possible channels. In fact, there is almost an order of magnitude enhancement in the yield of C 3 H 3 + when negatively chirped pulses are used, while there is no effect with the positive chirp. Moreover, the relative yield of all the other heavier fragment ions resulting from interaction of the strong field with the molecule is not sensitive to the sign of the chirp, within the noise level. Study of aromatic hydrocarbons has indicated different fragmentation channels (DeWitt et al., 1997). A systematic study of aromatic compounds with increasing chain-length of substituent alkyl groups has indicated that the fragmentation process is enhanced as the chain-length of the alkyl substituent on the benzene ring increases. We have chosen to apply chirped pulse fragmentation control on certain members of these systematically studied aromatic compounds. In general, as reported previously for benzene and toluene, p-nitro toluene, we also find that chirping favors the formation of smaller fragments as compared to the heavier ones. However, n-propyl benzene has the unique property of enhancing a particular fragmentation channel under the effect of chirp. We record the TOF mass spectra (Fig. 17) of n-propyl benzene using linearly chirped and unchirped ultrafast laser pulses with constant average energy of ~200 mW. Next, we compared the corresponding peaks in mass spectra by calculating their respective integrals Hot Chemistry with Cold Molecules 385 under the peaks and normalizing them with respect to the molecular ion. These results also conform to the case when we just compare the simple heights of the individual peaks. When the linear chirp of the laser pulse is negative, the relative yields of the smaller fragment ion, such as, C 3 H 3 + (mass to charge ratio, i.e., m/z = 39) is largely different from those obtained using transform-limited pulses or from the positively chirped pulses, as reflected in the Fig. . The relative yield of C 3 H 3 + reaches maximum when the linear chirp coefficient (β, calculated by using the equation as mention earlier) is -8064 fs 2 and pulse duration is of 450 fs. We would like to point out that the fragment ion C 6 H 5 + (m/z = 77) yield is more when the chirp is positive (β=+6246fs 2 ), and this can be attributed to a different fragmentation pathway (Fig.18). However, the observation of enhancement for only one chirp sign implies that the observed enhancements are not due to the pulse width effects, they rather depend on the magnitude and sign of the chirp. Hence coherence of the laser field plays an important role in this photofragmentaion process. It is also seen that relative yields of the heavier fragments like C 7 H 7 + (m/z = 91) is not affected by the sign of the chirp. 40 50 60 70 80 90 100 110 120 130 0.0 0.2 0.4 0.6 0.8 1.0 yield of fragment ions m/z transform limited β= 0fs 2 40 50 60 70 80 90 100 110 120 130 0.0 0.2 0.4 0.6 0.8 1.0 yield of the fragment ions m/z Negatively chirped pulse β= -8064fs 2 40 50 60 70 80 90 100 110 120 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 yield of fragment ions m/z positively chirped pulse β= +6246 fss 2 (a) (b) (c) Fig. 17. Effect of chirping on mass spectra of n-propyl benzene, (a) β=0 fs 2 , (b) β=-8064 fs 2 , (c) β=+6246 fs 2 . -10000 -5000 0 5000 10000 0.0 0.2 0.4 0.6 0.8 1.0 Relative Fragment ion yield & SHG intensity β (fs 2 ) C 3 H 3 + C 5 H 5 + C 6 H 5 + C 7 H 7 + SHG Fig. 18. Effect of chirping the laser pulse on the relative yield of different fragment ions shown in comparison to the integrated SHG intensity at the respective chirps. Laser Pulse Phenomena and Applications 386 The relative yield of C 7 H 7 + decreased in both the directions of the chirp and is at its maximum when the pulse is transform limited, indicating that the fragment yield only depends on the laser peak intensity as dictated by its pulse width. We have also seen that the integrated SHG intensity at different chirp is symmetrically decaying around 0 fs 2 (Fig. 18), which confirms that there is nothing systematic in the laser pulse causing the enhancements in the fragmentation process. 4. Conclusions We have built a molecular beam chamber with linear time of flight mass spectrometer, which can be combined with femtosecond laser in a novel way to study the femtosecond coherent control of supersonically cooled molecules. Our system is constructed with dryscroll pumps and turbo-pumps and is completely free from oil, which is very necessary for any femtosecond laser laboratory. In fact, this oil-free capability ensures that the obtained mass spectra is free from extraneous hydrocarbon peaks, which, in turn, makes our system better sensitive in studying coherent control of organic samples as reported in this book chapter. We have demonstrated that the phase characteristics of the femtosecond laser pulse play a very important role in the laser induced fragmentation of polyatomic molecules like n- propyl benzene. The use of chirped pulse leads to sufficient differences in the fragmentation pattern of n-propyl benzene, so that it is possible to control a particular fragmentation channel with chirped pulses. Overall, as compared to the transform-limited pulse, negatively chirped pulses enhance the relative yield of C 3 H 3 + , C 5 H 5 + , while the relative yield of C 6 H 5 + increases in case of positively chirped pulse. In fact, for the C 3 H 3 + fragment, the enhancement is almost 6 times for the negatively chirped pulse (β = -8064 fs 2 ) as compared to that of the transform-limited pulse. 5. References Rousseau, D. L. J. (1966). Laser chemistry, Chem. Educ., 43, 566-570. Smalley, R. E.; Wharton, L.; Levy, D. H. (1977). Molecular optical spectroscopy with supersonic beams and jets, Acc. Chem. Res., 10, 139-145. Levy, D. H. (1981). The spectroscopy of very cold gases, Science, 214, 263-269. Zewail, A. H. (1980). Laser Selective Chemistry: Is It Possible? Phys. Today, 33, 27. 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Rev., 107, 5082-5100. Herschbach, D. R. (1987). Molecular Dynamics of Elementary Chemical Reactions, Angew Chem. Int. Ed. Engl., 26, 1221-1243. Assion, A.; Baumart, T.; Bergt, M.; Brixner, T.; Kiefer, B.; Sayfried, V.; Strehle, M.; Gerber, G. (1998). Control of chemical reactions by feedback-optimized phase-shaped femtosecond laser pulses, Science, 282, 919-922. Daniel, C.; Full, J.; Gonzalez, L.; Kaposta, C.; Krenz, M.; Lupulescu, C.; Manz, J.; Minemoto, S.; Oppel, M.; Rosendo-Francisco, P.; Vajda, Š.; Wöste, L. (2001). Analysis and control on η 5 -CpMn(CO) 3 fragmentation processes, Chem. Phys., 267, 247-260. Levis, R. J.; Rabitz, H. A. (2002). Closing the Loop on Bond Selective Chemistry Using Tailored Strong Field Laser Pulses, J. Phys. Chem. A, 106, 6427-6444. Daniel, C.; Full, J.; González, L.; Lupulescu, C.; Manz, J.; Merli, A.; Vajda, S.; and Wöste, L. (2003). Deciphering the reaction dynamics underlying optimal control laser fields, Science, 299, 536-539, Weinacht, T. C.; White, J. L.; and Bucksbaum, P. H. (1999). Towards Strong Field Mode- Selective Chemistry, J. Phys. Chem. A, 103, 10166. Itakura, R.; Yamanouchi, K.; Tanabe, T.; Okamoto, T.; and Kannari, F. (2003). Dissociative ionization of ethanol in chirped intense laser fields. J. Chem. Phys. 119, 4179. Melinger, J.S.; Gandhi, S.R.; Hariharan, A.; Tull, J.X.; Warren, W.S. (1992). Generation of narrowband inversion with broadband laser pulses, Phys. Rev. Lett., 68, 2000-2003. Krause, J. L.; Whitnell, R. M.; Wilson, K. R.; Yan, Y.; Mukamel, S. (1993). Optical control of molecular dynamics: Molecular cannons, reflectrons, and wave-packet focusers, J. Chem. Phys. , 99, 6562. Cerullo, G.; Bardeen, C. J.; Wang, Q.; Shank, C. V. (1996). High Power Femtosecond Chirped Pulse Excitation of Molecules in Solution, Chem. Phys. Lett. 262, 362-368. Pastirk, I.; Brown, E. J.; Zhang, Q.; and Dantus, M. (1998). Quantum control of the yield of a chemical reaction, J. Chem. Phys., 108, 4375-4378. Yakovlev, V. V.; Bardeen, C. J.; Che, J.; Cao, J.; Wilson, K. R. (1998). Chirped pulse enhancement of multiphoton absorption in molecular Iodine, J. Chem. Phys., 108, 2309. Cao, J.; Che, J.; Wilson, K. R. (1998). Intra-pulse dynamical effects in multi-photon processes: Theoretical analysis, J. Phys. Chem., 102, 4284-4290. Guilhaus, M. (1995). Principles and instrumentation in time-of-flight mass spectrometry: Physical and instrumental concepts, J. Mass Spectrometry, 30, 1519-1532. Opsal, R. B.; Owens, K. G.; Reilly, J. P. (1985). Resolution in the Linear Time-of-Flight Mass Spectrometer, Anal. Chem., 57, 1884-1889. Mathur, D.; Rajgara, F. A. (2004). Dissociative ionization of methane by chirped pulses of intense laser light, J. Chem. Phys., 120, 5616. Lozovoy, V. V.; Dantus, M. (2008). Femtosecond laser-induced molecular sequential fragmentation of para-nitrotoluene, J. Phys. Chem. A, 112, 3789-3812. Laser Pulse Phenomena and Applications 388 Goswami, T.; Karthick Kumar, S. K.; Dutta, A.; Goswami, D. (2009). Control of laser induced molecular fragmentation of n-propyl benzene using chirped femtosecond laser pulses, Chem. Phys. 360, 47-52. DeWitt, M. J.; Peters, D. W.; Levis, R. J. (1997). The Photoionization/Dissociation of Alkyl Substituted Benzene Molecules Using Intense Near-Infrared Radiation, Chem. Phys. 218, 211-223. 19 UV-Laser and LED Fluorescence Detection of Trace Organic Compounds in Drinking Water and Distilled Spirits Anna V. Sharikova and Dennis K. Killinger University of South Florida USA 1. Introduction Current methods for the analysis of drinking water and many other liquids often call for the use of reagents and may require extensive sample preparation (American Public Health Association, 1989). For the case of water supplies and water treatment plants, this analysis is usually carried out once every few days or weeks (Killinger & Sivaprakasam, 2006). Most of the analysis is usually conducted using classical analytical chemical techniques, such as mass spectrometry, liquid chromatography, or fluorescence based or tagged reagents (Crompton, 2000). These analytical techniques are sensitive and provide accurate assessment of the chemistry related to the quality of the liquids. However, they often take considerable time and are usually not performed in real-time, especially for the case of a flowing process line. On the other hand, previous fluorescence spectroscopic measurements of ocean water by Coble showed that deep-UV excitation of naturally occurring organic compounds in water can yield significant and unique fluorescence signals in the near UV to visible wavelength range without the need to use additional reagents or sample preparation (Coble, 1996; Coble, 2007). As a result, we have been studying deep-UV laser-induced-fluorescence techniques for the detection of trace species in water and other liquids with the goal of using the natural fluorescence of trace species in the water or liquid samples and being able to provide readings within the time span of a few seconds. Toward this goal, we have developed a reagentless deep-UV laser and UV-LED induced fluorescence (LIF) system to detect and continuously observe in real time trace levels of colored dissolved organic matter (CDOM) or Dissolved Organic Compounds (DOCs) in water and distilled spirits, such as drinking water, and related water/alcohol based liquids with a sensitivity exceeding that of commercial spectrofluorometers. Our system has been used to detect ppb trace levels of plasicizer Bisphenol-A (BPA) that have leached into drinking water, and has detected and monitored trace levels of DOCs within ocean currents (Killinger & Sivaprakasam, 2006; Sivaprakasam et al. 2003; Sivaprakasam & Killinger, 2003). Recently, our LIF system has been used to measure fluorescence of reverse osmosis processed water and different types of drinking water (Sharikova & Killinger, 2007; Sharikova & Killinger, 2010). These LED/LIF applications have now been extended to additional water related samples, including humic acid samples, tannic acid and chlorinated water samples, juices, coffee, and several wines and distilled spirits; these recent results are presented in this paper. Laser Pulse Phenomena and Applications 390 Our compact LIF system used either frequency tripled or forth harmonic diode pumped Nd:YAG lasers operating at 266 nm and 355 nm, or deep-UV LEDs (265 nm, 300 nm, 335 nm, and 355 nm) as UV excitations sources. The emitted fluorescence was measured over the range of 240–680 nm. Strong emission near 450 nm was observed for the DOCs in water, while emission bands near 340 nm were evident from distilled spirits and wine. It is important to note that one of the main advantages of using a deep-UV excitation wavelength, such as 266 nm, is that the emission fluorescence is separated in wavelength from the Raman emission of water (near 310 nm for 266 nm excitation), and thus yields greater sensitivity and wavelength selectivity than previous systems using lasers operating near 400 to 550 nm. In addition, as a point of reference, our laser based LIF system had a detection sensitivity for the fluorescence standard solution of quinine sulfate on the order of 0.1 ppb. The average laser power was approximately 30 times that of the LED, but differences in the signal intensity due to the difference in the laser and LED excitation intensity were consistent with theory. Our studies show that deep-UV light emitting diodes (LEDs) are good alternative light sources for our LIF system, which would make the apparatus cheaper and more compact. It should be noted that the research presented in this paper is directed toward the development of new optical spectroscopic measurement techniques which have the potential to offer enhanced capabilities over conventional water monitoring and liquid analysis. However, while its sensitivity has been shown to be in the sub-parts per billion for standard fluorescing compounds used in fluorescence research, such as quinine sulfate, it needs to be further quantified and evaluated against conventional analytical chemistry instruments before it can be used as an on-line analytical instrument for water monitoring. Such comparisons are currently being conducted and will be reported later. 2. Experimental setup Our Laser and LED induced fluorescence system is similar to that of a conventional spectrofluorometer, but has a sensitivity several orders of magnitude better. Commercial spectrofluorometers often use UV lamps and wavelength selecting spectrometers for the emission source, and single or double monochromators with Photo-multiplier Tubes or CCD detecting arrays for fluorescence detection (Albani, 2007). Often the signal processing is conducted using a chopped CW beam and lock-in amplifier signal detection. Our LIF system uses a high PRF (pulse-repetition-frequency) laser running at about 8,000 pulses/second as the excitation source (or a pulsed LED source running at about 330 pulses/second), and a high- speed boxcar integrator which detects and stores the fluorescence photon signal for each pulse. In addition, our system uses multiple excitation beams and double-pass collection optics to increase the fluorescence signal. Our past work has shown that this combination has enhanced the sensitivity of our laser-induced-fluorescence system by two to three orders of magnitude over conventional spectrofluorometers, depending upon the spectrometer and optical detector configuration used (Sivaprakasam & Killinger, 2003). Details of our current LIF system follow. 2.1 Description of the apparatus Our fluorescence measurements were performed using a system shown in Fig. 1. The schematic diagram of the apparatus is shown in Fig. 2. The light source was one of the following: a microchip laser, 266 nm or 355 nm (JDS Uniphase, Models NU-10110-100 and NV-10110), or a LED operating at 265 nm, 300 nm, 335 nm or 355 nm (Sensor Electronic Technology, Inc., UVTOP® series). A silicon APD photodetector (New Focus, Model 1621) [...]... Pahokee peat humic acid standard Leonardite humic acid standard 40 20 0 250 Distilled water 350 450 550 650 Wavelength, nm Fig 14( d) Fig 14 Fluorescence of humic substances with (a) 266 nm, (b) 300 nm, (c) 335 nm, and (d) 355 nm LED excitation 406 Laser Pulse Phenomena and Applications Fig 15 Schematic diagram of the CW laboratory bench-top LED-IF / LIF system Fluorescence of natural and drinking water samples... nm, (b) 300 nm, (c) 335 nm, and (d) 355 nm LED excitation 402 Laser Pulse Phenomena and Applications Fig 12 Fluorescence of various drinks in distilled water; 266 nm laser excitation 3.4 Humic substance standards Humic acid is a principal component of humic substances which are the major organic constituents of soil, humus, peat, coal, many upland streams, natural lakes, and ocean water It is usually... 404 Laser Pulse Phenomena and Applications Fluorescence intensity, arb units 30 Suwannee River NOM (natural organic matter) Pahokee peat humic acid standard 20 Leonardite humic acid standard 10 Distilled water 0 250 350 450 550 Wavelength, nm 650 Fig 14( a) Fluorescence intensity, arb units 40 Suwannee River NOM (natural organic matter) 30 Pahokee peat humic acid standard Leonardite humic acid standard... configuration or sample photobleaching in the case of the lasers UV -Laser and LED Fluorescence Detection of Trace Organic Compounds in Drinking Water and Distilled Spirits 395 (a) (b) Fig 6 Week long continuous tap water monitoring with 266 nm laser excitation: (a) running tap water; (b) recirculated tap water 396 Laser Pulse Phenomena and Applications Fluorescence intensity, arb units 150 Chattanooga,... Association, & Water Pollution Control Federation Standard methods for the examination of water and wastewater (17th ed.) 408 Laser Pulse Phenomena and Applications Albani, J R (2007) Principles and applications of fluorescence spectroscopy Oxford: Blackwell Publishing Carnahan, Robert (2006); Private Communication (University of South Florida, Department of Chemical Engineering) Coble, P G (2007),... dermatology, industrial (Goode, 2008) applications among others The image, presented in Fig 1, shows an OCT image of the human hand palm 410 Laser Pulse Phenomena and Applications The bibliographic data helps to convince the reader about OCT impact and its potential, a brief research was performed in the Web of Science database for the keyword "optical AND coherence AND tomography" Firstly, as shown Fig... filter wheels (CVI Laser, Models AB-302 and AB-304) The PMT signal was acquired by a gated integrator and boxcar averager unit (Stanford Research System, Model SR-250) Data collection and filter wheel control was handled by LabVIEW software through a computer interface unit (Stanford Research System, Model SR-245) and serial bus 2.2 Laser and LED characteristics The Q-switched microchip lasers produced... output power of the 265 nm LED (LED265) as a function of wavelength and of drive current This is a log plot of the intensity and shows that the out-of-band LED emission had a peak value of about 1% compared to the peak emission at 265 nm Fig 1 Experimental system: optics box (left) and electronics box (right) 392 Laser Pulse Phenomena and Applications Fig 2 Schematic diagram of the experimental apparatus... 250 350 450 Wavelength, nm Fig 14( b) 550 650 UV -Laser and LED Fluorescence Detection of Trace Organic Compounds in Drinking Water and Distilled Spirits 405 Fluorescence intensity, arb units 70 Suwannee River NOM (natural organic matter) 60 Pahokee peat humic acid standard 50 40 Leonardite humic acid standard 30 20 10 Distilled water 0 250 350 450 550 650 Wavelength, nm Fig 14( c) Fluorescence intensity,... Blackberry wine Blueberry wine 150 100 Pinot noir Riesling Sake 50 0 250 Distilled water 350 450 550 650 Wavelength, nm (b) Fig 10 Fluorescence of wine samples with (a) 266 nm and (b) 355 nm laser excitation 400 Laser Pulse Phenomena and Applications Fluorescence intensity, arb units 200 Sake 150 Pinot noir Blackberry wine 100 Riesling 50 Blueberry wine Distilled water 0 250 350 450 550 Wavelength, nm 650 . the laser pulse is constant within the bandwidth of the laser pulse and hence it is made sure that at optimal grating distances we get the shorter pulse which is transform limited. In Fig. 14a,. tannic acid and chlorinated water samples, juices, coffee, and several wines and distilled spirits; these recent results are presented in this paper. Laser Pulse Phenomena and Applications. chirping the laser pulse on the relative yield of different fragment ions shown in comparison to the integrated SHG intensity at the respective chirps. Laser Pulse Phenomena and Applications